1. Field of Invention
The present invention relates to a twin-shaft vacuum pump and a method of producing or forming the same.
2. Description of the Prior Art
Multi-shaft vacuum pumps such as, e.g., screw pumps are widely used in dry pump systems, in particular, in chemical industry and in semiconductor technology. They consist essentially of a housing with two, crossing each other bores, and two helical rotors arranged in respective bores and rotatable in opposite directions. The two rotors are intermeshing roll over each other in a contactless manner. The cooperation of the two rotors produces a pumping action. The to-be-delivered gas is sucked through an inlet at one side of the rotors and is displaced axially toward the outlet. Due to the decreasing pitch of the screw thread from the inlet to the outlet, compression of the gas takes place.
At a present state of the art, the rotors are formed as one-piece members. The rotors should be formed with a very high precision in order to achieve their effective behavior. For producing of the rotors, five-axes machine-tools should be provided. Both the manufacturing of the rotors and their testing is time-consuming and expensive. In order to reduce manufacturing costs, certain deviations from an ideal profile were accepted. However, the drawback of this consists in high back flow losses. The manufacturing possibilities significantly influence the shape of the helical profile (screw profile).
The use-oriented adaptation results in a change of the screw profile of the rotor and, therefore, influences programming of the machine-tools and, eventually, selection of an appropriate tool or tools.
In particular, within the scope of the development of a pump, many adaptations are required. This results in high expenditure of time and high manufacturing and testing costs.
A further drawback of the conventional pumps consists in that the selection of materials is limited because of a need to take into consideration machining properties of the material.
Accordingly an object of the present invention is to provide twin-shaft vacuum pumps with rotors which can be produced by a simple and cost-effective manufacturing process and which, at the same time, meet the requirements with respect to their precision and testing.
Another object of the present invention is to provide twin-shaft vacuum pumps with rotors which permit an adaptation of their profile to the requirements of their particular use.
A further object of the present invention is to provide twin-shaft vacuum pumps with rotors which permit to increase the material selection the rotors can be formed of.
A still further object of the present invention is a simple and cost-effective process of manufacturing of rotors of twin-shaft vacuum pumps.